Use jscs for style checking

Equivalent to the check in Core, using the same jscs configuration file: https://github.com/jquery/jquery/pull/1396

I made two separate commits: One to fix existing issues that the tool pointed out (first commit), one to actually add the grunt task.

Based on that, the tool seems pretty useful. It certainly doesn't cover everything, so for now won't replace manual reviews. But not having to deal with a bunch of those issues will be pretty nice already.

Fixing issues in a file that has dozens issues or more is pretty annoying. For that and for more extensive checks, [esformatter](https://github.com/millermedeiros/esformatter/pull/46) is still pretty promising.

For this PR, someone please take a look at the first commit and see if any of the changes are invalid. We don't want the tool to enforce anything that is against the style guide. I changed lines that still have other issues that the tool doesn't cover, please ignore those.